There are a variety of light-emitting elements having different configurations, light-emitting principles, and the like. Currently, organic electro luminescence (EL) elements are being put into practical use as one of the light-emitting elements.
An organic EL element is configured by laminating a supporting substrate, an anode, a light-emitting layer composed of an organic substance, and a cathode in this order. When a voltage is applied to the organic EL element, holes are injected from the anode, and electrons are injected from the cathode. In addition, the holes and the electrodes, which have been injected from the respective electrodes, combine with each other in the light-emitting layer so as to emit light.
Since it is difficult to obtain desired light-emitting characteristics, in the organic EL element configured only with an anode, a light-emitting layer, and a cathode, prescribed layers other than the light-emitting layer are usually provided between the anode and the cathode. For example, a hole injection layer, an electron injection layer, or the like is provided between the anode and the cathode as the prescribed layer. The hole injection layer is provided between the anode and the light-emitting layer in order to facilitate injection of holes from the anode. In addition, the electron injection layer is provided between the cathode and the light-emitting layer in order to facilitate injection of electrons from the cathode. The above organic EL element is formed by laminating the supporting substrate, the anode, the hole injection layer, the light-emitting layer, the electron injection layer, and the cathode in this order.
Generally, the electron injection layer is configured with an electron injection material which is unstable in an atmospheric air. For example, the electron injection layer is configured with Ba, BaO, NaF, and the like, and is usually formed in a vacuum atmosphere. In addition, the cathode provided on the electron injection layer is usually formed in a vacuum atmosphere in order to suppress deterioration of the electron injection layer which is unstable in the atmospheric air.
As such, in the related art, while it is necessary to introduce a vacuum atmosphere in order to form the electron injection layer and the cathode, the scale of an apparatus increases, or the process becomes complicated in order to produce the vacuum atmosphere. For example, in a roll to roll method, which is considered as a method to facilitate manufacturing of the organic EL element, it is necessary to maintain the entire apparatus including an apparatus in which flexible films are wound in a vacuum atmosphere in order to form the electron injection layer and the cathode in a vacuum atmosphere, and there is a problem in that the scale of the apparatus increases (for example, refer to Patent Literature 1).
Therefore, studies are being made to develop electron injection materials which are relatively stable in the atmosphere and facilitate injection of electrons from the cathode in order to enable formation of the electron injection layer without introducing a vacuum atmospheric air. As the electron injection materials, organometallic complexes are proposed, and, in techniques of the related art, an electron injection layer is formed by applying the above metallic complex so as to form a film (for example, refer to Patent Literature 2).